Typically, for a physical layer of a portable internet system of an OFDMA scheme, four ranging modes are defined, such as initial ranging, periodic ranging, hand-off ranging, and bandwidth request ranging. The bandwidth request ranging mode is used for a terminal to request a bandwidth to a base station, and all other ranging modes are used for a power control and an uplink synchronization acquisition between the terminal and the base station.
In addition, the ranging modes are used to allow the ranging PN code signal to be output simultaneously from a plurality of terminals, and selectively for each terminal depending on its operation.
On the other hand, the ranging PN code used for a portable internet system of the OFDMA scheme is generated by a characteristic polynomial as shown in Equation 1, and the number of ranging PN code symbols available in each ranging mode is determined at the time of establishing an initial system.G(x)=x15+x7+x4+x+1   (Equation 1)
The ranging PN code generator applies different initialization codes for different cells using cell ID numbers which are expressed as a combination of “00101011” and 7 bits (i.e., [s6:s0]).
For example, for the 144-bit-long ranging PN code, 256 ranging PN codes in total may be used for the whole ranging modes, and such ranging PN codes may be generated as follows.
Firstly, one long sequence generated through first to (144*(K mod 256))-th clock outputs of the ranging PN code generator is equally divided into K number of 144-bit-long codes, and they are used as symbols for the initial ranging mode.
Another long sequence is generated through (144*(K mod 256)+1)-th to (144*((K+L) mod 256))-th clock outputs of the ranging PN code generator, and it is equally divided into L number of 144-bit-long codes for usage as symbols for the hand-off ranging mode.
In addition, another long sequence is generated through (144*((K+L) mod 256)+1)-th to (144*((K+L+M) mod 256))-th clock outputs of the ranging PN code generator, and it is equally divided into M number of 144-bit-long codes for usage as symbols for the periodic ranging mode.
Finally, another long sequence is generated through (144*((K+L+M) mod 256)+1)-th to (144*((K+L+M+N) mod 256))-th clock outputs of the ranging PN code generator, and it is equally divided into N number of 144-bit-long codes for usage as symbols for the bandwidth request ranging mode.
Conventionally, an apparatus for generating ranging PN code of a simple shift register generator (SSRG) scheme is used for the generation of such ranging PN codes.
FIG. 1 illustrates a schematic diagram of an apparatus for generating ranging PN codes of an SSRG scheme used for a wireless portable Internet system.
As shown in FIG. 1, a ranging PN code generator having an initial value (seed) of [0, 0, 1, 0, 1, 0, 1, 1, s0, s1, s2, s3, s4, s5, s6] generates a ranging PN code having a (144*A)-bit offset when receiving (144*A)-numbered clock signals corresponding to the offset information. Therefore, the apparatus for generating ranging PN codes of an SSRG scheme shows a drawback of consuming a significant amount of time to produce a desired result when a required offset value is high.
The ranging PN code used by a terminal is selected randomly within a range determined by a system with respect to respective ranging modes.
In summary, an apparatus for generating a ranging PN code of an SSRG scheme shows a drawback of needing a significant amount of memory in that it generates a desired ranging PN code at each offset by an application of clock signal thereto or it stores every possible state value thereof to generate the ranging PN code in response to cell ID numbers of all base station that a terminal can access.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention, and therefore, unless explicitly described to the contrary, it should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known in this country to a person of ordinary skill in the art.